Beta-adrenergic receptor subtype-specific signaling in cardiac myocytes from beta(1) and beta(2) adrenoceptor...

The sympathetic nervous system modulates cardiac contractility and rate by activating beta-adrenergic receptors (beta AR) expressed on cardiac myocytes and specialized cells in the sinoatrial node and the conduction system. Recent clinical studies have suggested that beta-adrenergic receptors also play a role in cardiac remodeling that occurs in the pathogenesis of cardiomyopathy. Both beta(1) and beta(2) adrenergic receptors are expressed in human and murine hearts. We have examined the effect of beta AR activation on the spontaneous contraction rate of neonatal myocyte cultures from wild-type and beta receptor knockout (KO) mice (beta(1)AR-KO, beta(2)AR-KO and beta(1)beta(2)AR-KO mice). Stimulation of the beta(1)AR in beta(2)AR-KO myocytes produces the greatest increase in contraction rate through a signaling pathway that requires protein kinase A (PKA) activation. In contrast, stimulation of the beta(2)AR in beta(1)AR-KO myocytes results in a biphasic effect on contraction rate with an initial increase in rate that does not require PKA, followed by a decrease in rate that involves coupling to a pertussis toxin sensitive G protein. A small isoproterenol-induced decrease in contraction rate observed in beta(1)beta(2)AR-KO myocytes can be attributed to the beta(3)AR. These studies show that all three beta AR subtypes are expressed in neonatal cardiac myocytes, and the beta(1)AR and beta(2)AR couple to distinct signaling pathways.